You can do it, but it's a bit tricky, due to the asynchronous nature of the
request.
What I did is that I pass a "callback" (I reused the ValueUpdater
interface, even though it's not about updating the value, but the method
signature was exactly what I needed) to the cell; see below.
You also need a cache for the retrieved data, as the cell can be
re-rendered at any time.
The idea is:
1. ask the cache (you can use the Cell.Context.getKey() as the cache
key, or any ProvidesKey for the value being rendered, or the value itself)
2. If the value was present in the cache, render it
3. Otherwise, fire the request and render something in the mean time
(e.g. "loading…")
- when the result comes back, put it into the cache and ask to be
re-rendered; this is where I use my ValueUpdater: I simply call the
updater's update(), and the view that uses the Cell then decides how to
do
it (in my case, I have a ListDataProvider, so it's as easy as
list.set(list.indexOf(value), value); –yes, replacing the value with
itself, it's enough to trigger a repaint–)
- When the Cell will be re-rendered, the value will be in the cache,
so the step #2 above will be triggered, instead of step #3, and the
retrieved value will be then rendered.
I guess you could also generate a placeholder with a unique ID (using
Document.get().createUniqueId()) the first time, and then use
Document.get().getElementById() and DOM manipulation (could be as simple as
a setInnerHTML) to update the value when the response comes back from the
server; instead of triggering a repaint.
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